/Engine/Source/Runtime/Engine/Classes/Kismet/KismetMathLibrary.h
Returns a random vector with length of 1, within the specified cone, with uniform random distribution. The shape of the cone can be modified according to the yaw and pitch angles.
static FVector RandomUnitVectorInEllipticalConeInDegrees ( FVector ConeDir, float MaxYawInDegrees, float MaxPitchInDegrees )